A film known from U.S. Pat. No. 3,741,253 to Brax comprises a core layer of a vinylidene chloride copolymer (saran) between a layer of ethylene-vinyl acetate copolymer and layer of a cross-linked ethylene-vinyl copolymer. Ethylene-vinyl acetate copolymer (EVA) has some improved properties over the previously used polyethylene. Vinylidene chloride copolymers are known barrier materials to fluids such as oxygen.
As disclosed in U.S. Pat. No. 4,064,296 to Bornstein, the core layer may also be a hydrolized ethylene-vinyl acetate copolymer (EVOH). It has similar oxygen barrier properties as vinylidene chloride copolymers and offers the advantage that it may be irradiated without discoloration, which is further discussed below.
U.S. Pat. No. 4,640,856 to Ferguson et al, commonly assigned to W. R. Grace, discloses a multi-layer, thermoplastic barrier film having at least threw layers comprising: (a) a layer consisting essentially of very low density polyethylene having a density of less than 0.910 gms/cc; (b) a barrier layer comprising a material selected from the group consisting of: (1) copolymers of vinylidene chloride and (2) hydrolyzed ethylene-vinyl acetate copolymers; (c) a thermoplastic polymeric layer, said layer being on the side of the barrier layer opposite to that of layer (a); and (d) the shrinkage of layer (a) controlling the shrinkage of the entire multi-layer barrier film said multi-layer film having been oriented and rendered heat shrinkable at a temperature below 100.degree. C. (212.degree. F.), said orientation temperature being about 40.degree. F., or more below the melt temperature of said very low density polyethylene.
U.S. Pat. No. 4,801,486, Quacquarella and Williams, assignors to W. R. Grace & Co.-Conn., discloses a multi-layer thermoplastic packaging film having improved heat shrink and cold seal properties, said film comprising:
(a) a first surface layer which is a heat sealing surface, said layer comprising; PA1 (b) a second surface layer, said layer comprising a polymer selected from the group consisting of amide polymers, ethylene/vinyl-acetate copolymers, the copolymer of the first layer, and ionomers; PA1 (c) a first core layer comprising an ethylene/vinyl-acetate copolymer; PA1 (d) a second core or barrier layer comprising a polymer selected from the group consisting of copolymers of vinylidene chloride and hydrolyzed copolymers of ethylene/vinyl-acetate; PA1 e) said core layers being internal film layers positioned between said first and second surface layers; PA1 (f) at least one adhesive layer to promote adhesion of the barrier layer to another layer; and PA1 (g) said film comprising at least five layers.
(1) a copolymer of ethylene and an alpha-olefin having 4 to 8 carbon atoms per molecule; and, PA2 (2) said copolymer comprising 90% to 75% ethylene and 10% to 25% alpha-olefin having 4 to 8 carbon molecules and a density of less than 915 kg/m.sup.3 ;
European Patent Application Publication Number 0292894 published Nov. 30, 1988 to Lustig and Schuetz, assignors to Viskase, discloses a coextruded, heat-shrinkable multi-layer film for packaging fresh red meat cuts and processed meats. The film comprises a first layer comprising very low density polyethylene a first core layer of vinylidene chloride-=methyl acrylate copolymer, and a second layer comprising very low density polyethylene. In another embodiment the first layer is a second core layer confined between said first core layer and a first outer layer comprising a heat sealable thermoplastic polymer or copolymer. In a further embodiment the second layer is a second core layer confined between said first core layer and a second outer layer comprising a thermoplastic polymer or copolymer.